1. Field of Invention
The invention concerns a bag machine for production of bags made of paper material and a method for production of bags from paper material.
2. Description of the Prior Art
Such bag machines have long been known. Unexamined Patent Application DE 35 29 746 A1 gives a good overview of such machines. The production method for paper bags is also described here.
Bag machines generally initially include an unwinding device, in which sheet-like paper material is unwound. The material is then fed in a conveyor device to the actual bag machine. In a first processing step, which is conducted in a corresponding station, the sheet material is provided with cross-perforations or crosscuts, so that weakening lines are formed. A cutting and/or perforation tool is generally mounted on a rotating shaft for this purpose. This tool enters the sheet-like material, which is running over a mating-roll, in which case the weakening lines are formed. The paper material can be separated into sections along these weakening lines. The distance between two weakening lines therefore establishes the length of the bag. Separation into sections generally occurs after passing through a tube-forming station, in which the side areas of the sheet-like paper material are folded to form an overlapping area, in which the facing sides of the overlapping area are joined to each other, for example, by applying an appropriate paper glue. The wall of the tube material, including the longitudinal seam formed in this way, is generally referred to as the upper wall of the tube or tube section. The other wall is referred to as lower wall accordingly. It is also possible to insert gussets into the tube. Gusset formation preferably occurs together with actual tube formation. Before joining to a tube, the later overlapping area must be coated with glue, for example, starch glue, for permanent joining.
Once a tube is formed, the tube must be separated in the separation device to tube sections along the weakening lines.
An individual weakening line can have only perforations, but according to DE 35 29 746 A1 mentioned in the introduction, it can also include smooth cuts. A weakening line then generally includes several sections that assume different positions viewed in the transport direction, i.e., are offset relative to each other. The trend of the weakening line is then chosen, so that the end of the lower wall in front protrudes over the upper wall in front. In this way, it is possible in the subsequent process to fold the lower wall onto the upper wall, so that the inside of the lower wall comes to lie on the outside of the upper wall. For actual bottom formation, the part being folded is provided with glue before folding. In the trailing end open in the later bag, the upper wall then protrudes beyond the lower wall. In certain bags, however, before or during the separation process to individual tube sections, a section of the upper wall is additionally removed, so that even in the trailing end, the lower wall protrudes beyond the upper wall. The part of one wall protruding beyond the other wall is referred to as the tab. In the preamble of Claim 1, the wall, whose trailing end has the tab, is referred to as first wall, in which this applies, regardless of whether the wall is the upper wall or the lower wall.
Bags for numerous applications are produced in the described manner. If a product to be transported is filled into the bag, such a bag is generally closed. After filling, the upper end is often simply folded, repeatedly folded or rolled. To avoid independent recovery of these folds, these folds are often secured with an adhesive film strip applied manually. It was recognized that adhesive film strips are often not on hand when they are needed. Bags are therefore known, on which an adhesive surface was already applied to an outer wall during the manufacturing process. In order to securely close such a bag, only the protective layer protecting the adhesive surface, for example, a coated and therefore less adherent paper piece, need be pulled off and the open end of the bag folded once, so that the outer wall then lies on itself or the tab lies on the adhesive surface. It must then be kept in mind that the end of the bag covers the adhesive surface precisely. If the end is folded too short, areas of the adhesive surface are not covered. On the other hand, if the end is folded too far, the end itself is not fixed.
The bag can therefore be inadvertently reopened, for example, if it hangs up on other objects.
If the bag is to be correctly closed, essentially just a single format of the closed bag is obtained. However, this is often undesired, when the bag is only partly filled. In this case, it is therefore desirable to be able to fold the end so that the format of the filled bag is no larger than necessary. However, this is not possible with bags of the prior art, if they are supposed to offer the capability of being securely closed.